Radio direction finder



Mardi 3 l94?- G. B. HAGEN 2,275,296

RADIO DIRECTION FINDER Filed Feb. 7, 1959 Snventor .Gerhard Hagen Bg f -(ftorneg -finder.

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2,275,296 RADIO DIRECTION FINDER Gerhard B. Hagen, Berli TelefunkenGesellscha n, Germany, assignor to ft fr Drahtlose Telegraphie m. b. H.,Berlin, Germany, a corporation of Germany Appiieation February InGermany 1 Claim.

This invention relates to a direction finder, especially to 'a so-calledicker-type direction In such direction finders two or more directivereceiving characteristics are produced by periodically switching theantenna circuits.

The flicker direction finder operates essential- `ly as follows: Whenthe receiving loop is in the proper direction-finding position, constantamplitude signals arereoeived. When the receiving loop is turned `out-ofthis position, `iiicker reception takes place, i.,e., amplitude of thereceived signal iiuctuates periodically. Such periodic variations of thelreceived signal are obtained by coupling a suitably tuned aerialcircuit with a loop Whose polarity is varied periodically at the desiredrate. The periodic coupling of the loop `or -the aerial circuit ispreferably altered at such vrl'iythni `or `rate that it will be possibleto tell by the sound of the received signal whether there has been adrift to the right or to the left-hand side of the proper course. It isparticularly advantageous to cause such change in coupling at the rhythm`of complementary telegraphic signals so that the proper course will beindicated by V,an uninterrupted dash, while course departures areindicated by a predominating signal, for example, `A -er N. Additionalto this course indication, it is necessary to determine whether thereceiver is approaching or passing away from the transmitter. Thisdetermination may be made by turning the loop out of zero reception andobserving whether the indicator shows a course departure correspondingto the loop movement or opposite thereto. This determination is notalways free from errors, which are f an immense danger for the airtraffic.

According to the present invention, the arrangement for the courseindication is combined with an arrangement for determining automaticallywhether the transmitter is fore or aft of the aircraft. For this reason,I have built a switching arrangement for the frame or aerial circuit,which gives periodically after a switching period for the courseindication a period for the fore or aft determination. The switchingdevice includes three switch positions: In the first two switchpositions the two conventional diagrams for the course indication areproduced; in the third position a diagram is produced, which identifiesthe fore or aft position of the transmitter. In the last switchingposition, a diagram may be produced which (by way of example) has itsmaximum reception ahead of the craft carrying the device, and itsminimum be- 7, 1939, Serial No. 254,994 February '1, 1938 (Cl. Z50-11)Cal hind the craft so that the fore and aft bearings may bedistinguished.

An arrangement of this Kind `shall be described with reference to thedrawing in which Figure l is a schematic circuit diagram of oneembodiment of the invention; Figure 2 is a schematic circuit diagram ofa modification; Figure 3 is an elevational View of the switching means;and Figure 4 is a graph of the several directive patterns. In theseveral figures, similar reference numerals will be used to indicatesimilar elements.

According to Fig. l, the aerial system consists of two crossed loops Iand Z and a nondirectional antenna i. A switch 3 is connected to theinput of the radio receiver 3. The switch has three different positionsQ, 5 and 5. In the first switch position 5s, loop l which is arranged atright angles to the proper course, is coupled to the input circuit ofthe receiver. In the second switch position 5, the same loop i iscoupled to the receiver input circuit, but with reversed phase. In thethird switch position 6, the second loop 2, which is arranged in thedirection of the proper course, is coupled to the input circuit of thereceiver 8. In combination with the nondirectional antenna. l in bothfirst switch positions, cardioid patterns are produced. Constant volumereception is obtained in the direction of equal energy of both patterns,as indicated by the intersection of the cardioids 25, 25 of Fig. 4.

In switch position G, in combination with the coupled nondirectionalantenna 1, a cardioid pattern is also produced, but that pattern isturned about 90 degrees to the aforesaid patterns. In Fig. 1, in whichmeans are represented for aural signals only, a transformer 9 isarranged in the output circuit of the receiver. The secondary of thetransformer has a midtap. By means of the switch lil in switch positionsand 5, the entire secondary voltage is applied to the telephones orother aural signal indicator Il. In the position 6 of the switch 3, theswitch lil is connected to the midtap so that only the half of thevoltage produced on the secondary of the transformer 9 is applied to theaural signal indicator Il.

For the purpose of explanation, reference is made to the field patternsshown in Fig. 4. The cardioid diagram 25 is obtained by combining thereceiving pattern 23 of loop I with the pattern 24 of aerial l. Thiscorresponds to position t of switch 3. In the same manner, the diagram26 may be obtained in switch position 5. The intersection of thepatterns 24-25 is the Vcontact segments.

course line, A, B. For the purpose of discrimination of both directionsA and B, the receiving pattern 22 of loop 2 is combined with pattern 24of the nondirectional antenna, 1. The resulting pattern is cardioiddiagram 21,4 the maximum of which is along direction A and the minimumalong direction B. It may be seen that the vector of the diagram 21 inthe direction A has twice the value of the vectors of either diagrams 25and 26 in the same direction. Thus, Ibecause of the output circuitswitching arrangement, the receiver output amplitude corresponding tothe course i-ndication is made equal to the amplitude corresponding tothe desired fore or aft indication, and a uniform signal will beobtained in the three positions 4, 5, 6 of switch 3, when the receivermoves along the course B, A in the direction of A. Y

The circuit may be used with a visual indicator as shown in Fig. 2. Thecurrent produced in the secondary of the transformer 9 is applied to arectifier I8. The rectified current is impressed through the rst andsecond positions I2 and I3 of the switchV I1 (corresponding respectivelyto the positions 4 and 5 of the antenna switch 3) upon the instrumentI5. In the third position I4 of the switch I'I, the rectified current isapplied to another instrument I6. This instrument I6 is used todetermine the fore or aft position of the transmitter. The thirdposition I4 of the switch I7 corresponds to the third position 6 of theantenna switch 3.

By way of example, one section of a suitable rotary switch arrangementis shown in Fig. 3. The switch consists of two rings 30, 32, arrangedconcentric to one another. Each ring has three Each of the switchpositions corresponding to switch positions 4, and 6 possesses a pair ofContact segments 20 and 2I. The

movable contact is a rotating brush I 9, which has also `two contacts.The contacts are insulated and connected by any suitable means to theinput of the receiver 8. The output switch I'I is arranged in a similarmanner.

The switch 3 may be operated in accordance with complementary Morsesignals e-t. When both received signals e and t have the same amplitude,the pilot is `on the proper course. If an additional e signal isreceived with the same amplitudevon switch position 6 of Fig. 1, thecarrying the device is on the proper course and the transmitter is infront. Of course, a method in any other rhythm may be proposed. But itis `necessary to choose a short sign Yfor switch posicraft I tion 6.Thereby it is possible to obtain a proper visual right-left indicationand la proper indication of the side of the transmitter. According toFig. 2, the switch I 'I is switched from instrument I5 to instrument I6on switch positions 6 and I 4. If the switching from the meter I 5results in any change of its indication, such effect may be compensatedfor by applying a suitable compensating current.

While I have shown and described my invention in certain specificembodiments, it will of course Ibe understood that I do not wish to belimited thereto. It is possible to provide other known antenna systemsfor the course indication, such as an Adcock system. In the specificembodiment, the course indication has been produced by theecardioidpatterns obtained periodically in the rst two switch positions, and inthe third switch position the pattern for the fore and aft determinationis produced. The switching may be also arranged so that one switchposition for fore and Iait determination is followed by iive switchingpositions for course indication. The

rotating switch must then be built in such manner that five segments e-tare followed by one segment e.

Having thus described my invention and the operation thereof, what Iclaim is:

A radio direction nder including in combination a directive antenna, asecond directive antenna angularly disposed with respect to said firstantenna, a nondirectional antenna, a radio receiver having input andoutput circuits, switching means including said radio receiver forcombining in successive order the currents of one of said directiveantennas with the currents of said nondirectional antenna to produce apair of antenna patterns whose intersections indicate a course and forcombining the currents of the other of saidV directive antennas with thecurrents of said nondirective antenna to produce a third antenna patternto indicate the fore or aft position of the transmitter establishing thecourse, means connecting the input circuit of said radio receiver tosaid switching means, means including a second switching means connectedto the output of said receiver, means for continuously operating saidrst and second switching means continuously and in synchronism, and apair of visual indicators connected to said second switching means forindicating successively and automatically said course and fore or aftposition.

GERHARD B. HAGEN.

